1. Technical Field
This invention relates generally to the field of very high power integrated power systems involving alternating current power generation coupled to alternating current or direct current power components, and more specifically, to an integrated ship power system with electric motor propulsion powered by a main turbine generator all controlled by a supervisory control and data acquisition system with externally adjustable power rate constraints that define an anticipatory mode design via new power control electronics. Applications are comprised of the field of ship propulsion, other large propulsion motors, or any variant wherein the load is significant, on a percentage basis, to the generation available such as electromagnetic launch of aircraft, high power microwave weapons and high power laser weapons.
2. Background Art
Integrated power systems involving alternating current and/or direct current high power components have traditionally been implemented with reactive system designs that operate stably only within a small range of power generation and consumption. One particular limitation has involved achieving stable power system operation when the desired dynamic changes in a high power load is not supported by the power system generation capacity. Current integrated power systems as designed can remain stable only by accommodating limited and relatively small changes to this power flow between the generator capacity and the power load demands.
As applied to an integrated ship power system with electric motor propulsion powered by a main turbine generator, the limitations of current reactive system designs limits selection of ship acceleration and/or the rate at which the ship velocity can be changed. Currently, ship accelerations are generally limited to normal, rapid and emergency rates, torques or power settings that a ship's captain can utilize for changes in the ship's velocity. Changes must be slow to minimize electrical transients due to the limitations of the reactive mode design. This is because the ship motor load demand can change more quickly than the steam valve controlling the main steam turbine and the steam turbine generator itself can respond. The inability of the steam turbine generator to respond as quickly as the ship motor load demand leads to electrical power system instability.
Additionally, present day motor controllers adjust ship velocity by maintaining constant motor speed, torque, or power and are not typically concerned with power rate demands placed on the turbine generator and this may lead to electrical instability. A potential solution, to slow down the motor controller response, is a novel nonlinear motor controller described by Sudhoff, et. al. in “DC Link Stabilized Field Oriented Control of Electric Propulsion Systems”, IEEE Transactions on Energy Conversion Vol. 13, No. 1, March 1998. Yet, this paper or others in the field, do not take advantage of a supervisory control and data acquisition system and solve the problem with a limited range of power rate constraints to the motor controller.
The current state-of-the-art is represented by a reactionary design: a new ship rate is obtained by a request that is intended to induce a higher speed (RPM) of the electric motor, where the motor load increases, which in turn slows down the electrical generator, and the governor to the main turbine generator then responds and increases steam to the turbine to provide more power. The electrical load forces the response of the turbine generator governor. This reactionary design has serious limitations due to the fact that the dynamic response of a high power inductive propulsion motor can be very much quicker than the dynamic response of the mechanical valves that control the turbine generator speed. This mismatch between the load reaction and electrical power generation leads to instability of the electrical power system. Defined by the present invention is an anticipatory control mode integral to the integrated power system with control provided by the supervisory control and data acquisition (heretofore referred to as SCADA). Applied to ship propulsion, this enhanced integrated power system introduces the possibility of anticipating, by way of computing, the transient response of the integrated power system to a proposed commanded change of ship velocity; that allows the system to implement externally adjusted power rate of change constraints that correspond to the commanded ship velocity change by precisely controlling the anticipated, and real-time, power flow between the main turbine generator and the propulsion motor and assures electrical system stability with increased range of ship rate of change control.
However, such a very high power integrated power system involving alternating current high power generation capacity coupled to highly dynamic large alternating current or direct current loads, all controlled by a SCADA system, with the ability to accept or define power rate constraints, has not been used in the field of ship propulsion, other large propulsion motors, or any variant wherein the load is significant, on a percentage basis, to the generation available such as electromagnetic launch of aircraft, high power microwave weapons and high power laser weapons. There are numerous reasons for this non-use, such as the availability of extremely high current control devices capable of integration into a distributed, computer controlled, high power alternating current or direct current power system. Additionally, in several industries, generally speaking, a SCADA system refers to a system that does not control processes in real-time, but rather coordinates processes. Currently, SCADA systems are then typically seen as distinct from distributed control systems and are not implemented as defined by the present invention.
While the above cited references introduce and disclose a number of noteworthy advances and technological improvements within the art, none completely fulfills the specific objectives achieved by this invention.